The present invention relates to a power and free conveyor system and, more particularly, to an improved mechanism for transferring a train of free trolleys through an area wherein no power is applied to the normal drive trolley.
Power and free conveyor systems normally include trains of interconnected load bearing trolleys which ride upon a load bearing track and are driven by a power conveyor device in the form of a chain. The power conveyor chains are normally of an endless variety, and it is often required that the individual power chain sections be shorter than the desired travel distance of the trolleys, thereby requiring several such power chain sections. It is sometimes desired to transfer the load to a side track wherein no driving power is applied to the train. In addition, many conveyor systems also have switching stations whereat two or more tracks diverge from a single track and/or it is advantageous to vary the speed of the trolley train within the system, thus requiring separate power conveyor chains. In most conventional power and free conveyor systems of the type described herein a dog depends from the power conveyor chain and engages a power trolley, normally the lead trolley, as long as the lead trolley is beneath the power conveyor chain. However, whenever the train transfers between two different power chains or transfers onto a track having no power chain associated therewith, the lead trolley is no longer beneath the power conveyor and has no power applied thereto, at least temporarily. Therefore, a system is necessary to positively effect the transfer of the trolley train across the transfer area wherein no power is applied to the lead trolley.
Conventional methods for powering the trolley train across the transfer area have included such devices as pneumatic air cylinders which are tripped at the appropriate time and push the trolley train across the gap and/or downwardly sloping tracks wherein gravity is used to effect the transfer. The pneumatic devices along with other similar devices require complex machinery are usually expensive and machinery difficult to maintain. The downwardly sloping tracks also tend to be expensive in addition to being difficult to engineer and inappropriate for placement in many conveyor systems.
Another method for powering the trolley train across the transfer area includes: engagement of the original power conveyor chain by a trailing trolley after the power trolley has disengaged therefrom, driving the trolley train across the gap by means of this engagement of the trailing or transfer trolley and the original power chain, and disengaging the original power chain from the trailing trolley upon engagement of the power trolley with the second chain. An example of such a system is disclosed in the U.S. patent to Robert A. Hoehn, No. 4,072,111. The Hoehn system utilizes a cam depending from the upper flange of and into the track and a transfer dog pivotally attached to an upper part of the transfer trolley and having a cam follower on one end suitable for following the cam and raising the opposite end of the transfer dog into a position to engage the first power chain. The cam is selectively positioned such that the transfer dog is raised throughout the period required for transfer of the trolley train across the gap between the two power conveyor chains.
The Hoehn transfer system functions well for many types of conveyor systems; however, as the conveyor track, and hence trolley, becomes smaller the individual pieces thereof must be reduced in size. For small conveyor systems, the Hoehn device becomes structurally weak and difficult to engineer within the small volume available between the sides of the track of such smaller systems. Therefore, a transfer mechanism is desired which would be located substantially outside of the track. In addition, it is desired that no part of the transfer system extend above the track except when the actual transfer is taking place, thereby eliminating possible snagging by structural supports or by the power conveyor chain when such is not desired.